Radioactivity Induced by Nuclear Excitation II. Excitation by Protons

Radioactive indium resulting from proton bombardment of indium exhibits negative electron emission which decays with a 4.1-hr. half-life. Proton bombardment of cadmium does not produce this activity. It is ascribed to a metastable excited state of ${\mathrm{In}}^{115}$ designated by ${\mathrm{In}}^{115*}$ formed by a new type of proton excitation process. Control experiments exclude the possibility of its being formed by stray neutrons. The cross section for protons of 5.8 Mev is about ${10}^{-29\mathrm{}}$ ${\mathrm{cm}}^2$.